Let π be a self-dual irreducible cuspidal automorphic representation of GL2 (AQ) with trivial central character.Its Hecke eigenvalue λπ(n) is a real multiplicative function in n.We show that λπ(n) < 0 for some n << Q2/5π,where Qπ denotes (a special value of) the analytic conductor.The value 2/5 is the first explicit exponent for Hecke-Maass newforms.